Currently the Maintenance Complete Email Notification option found under Setup > Company > General Preferences is sent only to all active Account Administrators on an account.
Customers that want this Notification to also be sent to Non-Administrators may consider the following Alternate Solution:
Have one of the Administrators that receive these emails:
1. Set up a group in Outlook that holds all the other users that this notification is to be sent to.
2. Then create a rule in Outlook that when an email is received from the NetSuite address with the Subject used for these Notifications have it automatically forward to this group.